What Does a Trailing Arm Do?
A trailing arm is part of an automobile's suspension. It is normally located forward of the rear axle and connects the axle to the car chassis. It is a relatively large piece of the suspension that supports the coil springs. When driving down a bumpy road, the trailing arm moves up and down to smooth the ride.
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Original Rigid Trailing Arm
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Even though the trailing arm does a good job at smoothing out bumps on a road, it does not allow for lateral movement, or side sway. When a car negotiates a turn, especially at highway speed, the car body will roll into the turn and so will the trailing arm. This flaw will cause the wheels to lean to the outside of the turn, resulting in under-steering. For this reason, the original rigid trailing arm was dropped by auto makers for the newer semi-trailing arm.
Semi-Trailing Arm
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The semi-trailing arm is basically the same as the trailing arm except the arms on either side of the axle are pivoted at angles between 50 and 70 degrees. When a car goes into a turn with the semi-trailing arm, these pivoted angles have a canceling effect on each other, eliminating the under-steer. The disadvantage is that when the arm moves up and down in response to bumps, it changes the camber angle to the wheels, which can lead to uneven tire wear. Torsion beam and MacPherson strut suspensions have corrected this problem.
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Bushings
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Whether you have a car with trailing arms or semi-trailing arms, the arms connect to the axle and the chassis with bushings, and they will wear out. A qualified mechanic can visually inspect the bushings for unusual cracking or wear. A can that doesn't handle well while cornering might also require bushing replacement.
Anti-Roll Bar
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Some trailing arms come with anti-roll bars specifically designed to counteract the corner sway generated from highway cornering. This sway bar attaches to the lower portion of the trailing arm, usually with four bolts.
Replacement Cost
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Depending on what year and make of car you drive, replacing your worn-out trailing arm and bushings can cost from a couple hundred to several hundred dollars. Car owners who are mechanically inclined can save a lot of labor expense by installing the new arms themselves.
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